Adsorptive separation to remove contaminants from gas streams, particularly organic contaminants, is frequently used in chemical processing.
As adsorbents are used, they periodically require regeneration. During regeneration of an adsorbent, the adsorbent is conventionally heated and brought into contact with a regenerating gas stream. The adsorbed components thereby dissolve in the regenerating gas stream and the adsorbent is unloaded.
A process for the catalytic oxidation of HCl gas is described in European Patent No. EP 233 773 B1, in which a HCl gas contaminated with organic impurities such as benzene, chlorobenzene and the like is prepurified for use in a Deacon process (catalytic HCl oxidation by means of oxygen). In the prepurification described therein, activated carbon is used as the adsorber and is regenerated after use. It is further proposed to regenerate the adsorber at elevated temperatures or under reduced pressure and optionally using an inert gas.
Depending on the organic load of the gas stream that is to be purified and on the vapor pressure of the organic components that are to be separated off, the use of a low-temperature condensation provided upstream of the adsorption process can be economically advantageous in some instances. In such processes, a major part of the organic load can be separated off in a condensation system, while after-purification to the required purities can take place with the aid of an adsorption step.
Such a combination of condensation and adsorption is described, for example, in U.S. Pat. No. 5,740,682. As discussed therein, for example, hydrocarbons are removed from air.
However, in a process for removing organic components from HCl gas streams, the above-described combination of low-temperature condensation and subsequent adsorption may result in a significant amount of HCl and phosgene which may be present in the gas stream being dissolved in the organic components separated off by the condensation. The dissolution of those components would then give rise to significant subsequent costs for the conversion of phosgene and HCl into sodium chloride and sodium carbonate via sodium hydroxide. At the same time, the amounts of phosgene and HCl discharged from such a process would represent a not inconsiderable chlorine loss, which is undesirable in particular in a process with a chlorine circuit.